1. Field of the Invention
This invention is concerned with extending the useful life of zeolite catalysts by reducing coke formation and aging rate.
2. Description of the Prior Art
Crystalline zeolite catalysts are widely utilized in many important and industrially significant processes. They are used in the petroleum industry in the refining of crude oil into lighter fractions, catalyzing such reactions as cracking relatively large or undesirably branched molecules into more useful smaller molecules, reforming or restructuring molecules into other molecular structures having other more desirable utility, and in aromatization reactions (i.e. the conversion of paraffins and olefins to aromatic compounds), to name just a few. The chemical industry also utilizes these rather amazing catalysts in similar types of reactions to produce materials which had previously been relatively difficult or even impossible to manufacture by conventional non-zeolite technology.
One of the limitations of zeolite catalysts has been its tendency to "age" or lose its high level of activity with time. This has been attributed to the formation of undesirable carbonaceous deposits or "coke" on the catalyst's active sites during hydrocarbon conversion reactions. The problem seems to be exacerbated when the zeolite catalyst is carried on a binder material which itself may contribute to the cracking reaction to produce more coke. Aluminum oxide, which is a very commonly used binder for zeolite catalysts, is a particularly noteworthy offender in this respect. Once the carbon deposits have reached the point where the reaction level becomes economically undesirable, the only known way to correct the problem has been to shut down the reactor and burn the carbon off of the catalyst in an oxygen-containing atmosphere. This, needless to say, is an expensive operation which one would rather not have to resort to any more frequently than absolutely necessary.